The gut is now recognized as the second “brain” in our body. The newest research suggests that foods containing probiotics (live bacteria and microorganisms) can lower stress, anxiety, and depression in rats and possibly humans.

The gut can release neurotransmitters regulating many brain functions. Mice dosed with probiotics showed differences in brain chemistry, too. Bacteria-fed mice had half as much stress hormones in their blood, compared to the control group. The bacteria also seemed to cause redistribution of GABA, a neurotransmitter, in a way similar to taking valium. Although research is too early to definitive, you may be able to eat your way to happiness. The brain/gut connection is essential for mental health: when the researchers snipped the vagus nerve of mice, the benefits disappeared. "It's pretty convincing," says Brett Finlay, a microbiologist at the University of British Columbia in Vancouver, Canada. "These days our microbiota are being implicated in just about everything."

Previous work has shown that probiotics can improve the moods of patients with chronic fatigue syndrome. In another study, people given Lactobacillus helveticus and Bifidobacterium longum improved mental health scores in healthy volunteers.